This invention relates to a hydrogen storage apparatus for use with a vehicle that utilizes hydrogen as a fuel (hereinafter referred to as xe2x80x9chydrogen-fueled vehiclexe2x80x9d).
In recent years, a tank for storing liquid hydrogen as a fuel is used as a hydrogen storage apparatus for a hydrogen-fueled vehicle. In the hydrogen-fueled vehicle including such a tank, the liquid hydrogen filled into the tank is gasified, and thus increases pressure in the tank, which makes it difficult to fill liquid hydrogen into the tank, disadvantageously making the hydrogen-filling operation a time-consuming task. Therefore, the gasified hydrogen (hereinafter referred to as boil-off gas or xe2x80x9cBOGxe2x80x9d) is usually degassed out of the vehicle, as appropriate, so as not to keep the pressure in the tank from increasing beyond a predetermined level.
However, such a conventionally adopted process of degassing BOG out of the vehicle in turn causes the fuel efficiency to decline by the amount of BOG degassed. Conversely, in order to keep the fuel efficiency from declining, the BOG degassed out of the vehicle should be restricted to the minimum, and restriction of the degassed BOG would disadvantageously prolong the time required to fill hydrogen.
Therefore, it is an exemplified general object of the present invention to provide a hydrogen storage apparatus and method of filling hydrogen into the hydrogen storage apparatus capable of shortening the filling time as well as enhancing the fuel efficiency.
According to one exemplified aspect of the present invention, there is provided a hydrogen storage apparatus including a liquid hydrogen tank, a hydrogen filling passage, a degassing passage, a hydrogen occlusive tank, and a cooling device. The liquid hydrogen tank is installed in a hydrogen-fueled vehicle driven by a hydrogen-using device. The hydrogen filling passage fills liquid hydrogen into the liquid hydrogen tank. The degassing passage is provided with a release valve that opens when pressure of hydrogen gasified in the liquid hydrogen tank reaches a predetermined actuating pressure. The hydrogen occlusive tank accommodates a hydrogen occlusive alloy for storing the gasified hydrogen. The pressure in the hydrogen occlusive tank when liquid hydrogen is being filled into the liquid hydrogen tank is lowered using the cooling device that cools the hydrogen occlusive tank.
When the liquid hydrogen is being filled into the liquid hydrogen tank, the cooling device cools the hydrogen occlusive tank, and thereby the pressure in the hydrogen occlusive tank decreases. When the pressure in the liquid hydrogen tank reaches the predetermined actuating pressure, the release valve opens and hydrogen gasified in the liquid hydrogen tank is flown into the hydrogen occlusive tank. Hydrogen, thus flown into the hydrogen occlusive tank, is occluded in the cooled hydrogen occlusive alloy. The actuating pressure may be an absolute pressure in the liquid hydrogen tank, and may also be a differential pressure between internal pressures in the liquid hydrogen tank and in the hydrogen occlusive tank.
According to another exemplified aspect of the present invention, the above cooling device in the hydrogen storage apparatus cools the hydrogen occlusive tank utilizing the liquid hydrogen that is being filled.
The temperature of the liquid hydrogen lower than the boiling point of principal components of air, nitrogen and oxygen, may for example cool air surrounding the hydrogen filling passage through which the liquid hydrogen passes, changing the air into the liquid state. The resultant liquid air is mixed with air and blown to the hydrogen occlusive tank using a blower such as a fan.
According to yet another exemplified aspect of the present invention, the above hydrogen storage apparatus further includes a bypass that is provided in the degassing passage so as to detour round the release valve, and a switching device that alternatively switches a route of the gasified hydrogen between the degassing passage and the bypass. The switching device switches the route to allow hydrogen gasified in the liquid hydrogen tank to pass through the bypass when liquid hydrogen is being filled into the liquid hydrogen tank.
When the liquid hydrogen is being filled into the liquid hydrogen tank, the switching device may be switched so as to allow hydrogen gasified in the liquid hydrogen tank to pass through the bypass, so that the hydrogen may bypass the release valve and be fed into the hydrogen occlusive tank.
According to yet another exemplified aspect of the present invention, the above hydrogen occlusive tank is connected to the hydrogen-using device, so that hydrogen in the hydrogen occlusive tank is used prior to hydrogen in the liquid hydrogen tank when the hydrogen-using device is driven.
Under conditions where the hydrogen occlusive tank may generate hydrogen and supply the same to the hydrogen-using device when the hydrogen-using device is driven, hydrogen is supplied from the hydrogen occlusive tank by priority.
According to yet another exemplified aspect of the present invention, there is provided a method of filling hydrogen into a hydrogen storage apparatus installed in a hydrogen-fueled vehicle driven by a hydrogen-using device, which hydrogen storage apparatus includes a liquid hydrogen tank and a hydrogen occlusive tank. The method comprises the steps of filling liquid hydrogen into the liquid hydrogen tank, and enabling the hydrogen occlusive tank to occlude hydrogen gasified in the liquid hydrogen tank, to reduce pressure in the liquid hydrogen tank. This method, which includes the step for reducing pressure in the liquid hydrogen tank, thus serves to accelerate the operation of filling liquid hydrogen into the liquid hydrogen tank, and shortens the filling time. Moreover, no BOG is degassed out by this method, and thus fuel efficiency is improved.
The above method may further include the step of cooling the hydrogen occlusive tank. Cooling the hydrogen occlusive tank contributes to secure reduction of the pressure in the liquid hydrogen tank.